This invention relates to a method of and system for determining imbalances in tire pressure on vehicles equipped with wheel rotation sensors.
Some suppliers of automotive chassis control systems offer algorithms that use wheel speed for pneumatic tire inflation monitoring. The typical wheel speed based tire inflation-monitoring algorithm resides within an anti-lock brake controller. This system architecture is required because of the need for high resolution and high wheel speed data throughput. These systems rely on accurate microprocessor timer information to perform the required speed calculations. The measured time between speed ring teeth is used to calculate wheel speed and wheel slip. Due to the nature of these calculations, such systems are prone to noisy data at low and high speeds, under some road conditions, due to imprecise machining of speed ring teeth, and microprocessor timing limitations. A typical wheel speed based system may operate well while traveling in a straight line, at steady speeds, and on smooth surfaces, but exhibit a high rate of false warnings when conditions are not optimal.
While a vehicle is in motion, the present invention determines when any combination of one, two, or three wheels are in a state of rotational error through an adaptive measurement of the distance that the four wheels have traveled and not through any calculation of wheel speed. This invention has the inherent ability to accurately discern a measure of pneumatic tire pressure imbalance in a way not yet achieved.
More precisely, this invention provides a means to accurately monitor tire pressure imbalance through the measurement of distance by way of digital pulse devices included in existing anti-lock braking systems and vehicle transmissions. Moreover, this invention does not use nor care about the measured time between digital pulses and will operate at the lowest possible speed at which a digital pulse may be sensed. This invention will operate and maintain accuracy equally as well at unrestricted high speeds. This invention will operate expediently on any surface. Tire pressure imbalance is determined while all four wheels are on a similar surface. Furthermore, this invention is able to detect certain surfaces such as gravel, snow, grass, etc.
The first step in this process is to compute a xe2x80x9cperfectxe2x80x9d average of the diagonal ratio (the ratio of pulses accumulated on one front and its opposite rear over the total pulses). This computation must be performed when the vehicle is traversing a non-deformable surface, has zero acceleration, and is going straight. This xe2x80x9cperfectxe2x80x9d average is then used to generate a tire deformation adjustment to compensate for acceleration, deceleration, or turning during data collection. This adjustment prevents the false triggering of a warning on tires that are lower than the nominal pressure, but still above the warning threshold. False triggering can be caused by the effect of weight transference due to acceleration, deceleration or cornering on tire rolling radius.
Three separate tests are performed to determine tire pressure loss. The first test covers any individual tire, opposing diagonal tires, or any combination of three low tires. The first step in this process is to compute an average of the diagonal ratio. A requirement of this test is that the diagonal ratio stays within a narrow band. If the diagonal ratio goes outside of the acceptable band, the data is deemed unreasonable, and is not included in the average diagonal ratio. In the case of a rapid loss of pressure, the data will be ignored initially, and then accepted when it meets the criteria of repeatability. If the data is deemed repeatable, the tire deformation adjustment is applied to it and a running average is formed. If the running average is greater than the calibration amount by more than the pressure loss threshold, a warning occurs. If the running average is less than the trigger point, a test is performed to determine if a warning is currently set. If no warning is set, the routine proceeds to the multiple wheel tests. If a warning is set, the routine checks for constant speed and heading. If this criterion is met, the diagonal ratio is tested for being within three PSI of the xe2x80x9cperfectxe2x80x9d average computed previously. If this condition is met, the warning is cleared.
The two additional pressure loss tests cover the loss of pressure from both of the front, rear, left, or right tires. These multiple wheel tests require that the vehicle is not accelerating, decelerating, or turning. The algorithm looks for repeatability over several tenths of a mile to determine low tires. The distance test must be set to accommodate the longest curve likely to be encountered. To perform this test, lateral and longitudinal distance ratios must be computed. The lateral ratio consists of the ratio of the pulses accumulated on one side of the vehicle to the total pulses. If the lateral or longitudinal ratios are greater than a calibration, then the routine resets the respective test odometer. When the longitudinal odometer counts down to zero, the longitudinal ratio minus a speed related compensation is compared to a pressure loss threshold. A warning occurs if the threshold is exceeded, and is cleared if the longitudinal ratio is within three PSI of the nominal calibration. When the lateral odometer counts down to zero, the lateral ratio is compared to a pressure loss threshold. A warning occurs if the threshold is exceeded, and is cleared if the lateral ratio is within three PSI of the nominal calibration.
The calibration mode is very strict about the data it will accept. It will not accept data during acceleration, deceleration, turning, or any non-repeatable data ratios. If the longitudinal ratio varies outside of a tight calibration, the algorithm rejects the data. If the vehicle is traversing a deformable surface, the routine rejects the data. If the data passes both of these tests, tight repeatability criteria insure that the measurement is valid. The data from the calibration mode is used to compensate the incoming data to eliminate the effects of variation in tire loading, tire size, tire wear that are normally present.
Moreover, this invention will accommodate any steering angle, longitudinal acceleration, or lateral acceleration. In addition, this invention uses an adaptive method to eliminate false warnings by tracking variations in tire pressure that are less than the warning trigger point and adjusting the measurements based on the tire deformation characteristics due to acceleration induced weight transference and/or vehicle load.
Advantageously, this invention will calibrate all four wheels during periods of zero longitudinal and lateral acceleration and adaptively correct for speed variations of all wheels.
Advantageously, this invention will trigger a warning upon reaching a predetermined pressure loss threshold and clear said warning without recalibration upon a tire reaching a predetermined recovery threshold. This is a self-clearing feature which clears the warning when a tire or tires are refilled to a predetermined level within the nominal calibration thresholds or when simply clearing a false trigger precipitated by a juxtaposition of unlikely data events.
Advantageously, this invention will trigger a warning upon the rapid loss of tire pressure. This will allow detection of all types of pressure leakage, from a pinhole leak to a catastrophic failure.
Advantageously, this invention may reside in any vehicle controller or custom built controller that may receive digital pulses from an ABS system and/or a vehicle transmission at any regularly scheduled time interval by any available form of communication.